Glaucoma is a collection of disorders characterized by progressive visual field loss due to optic nerve damage. It is the leading cause of blindness in the United States, affecting 1-2% of individuals aged 60 and over. Although there are many risk factors associated with the development of glaucoma (age, race, myopia, family history, and injury), elevated intraocular pressure, also known as ocular hypertension, is the only risk factor successfully manipulated and correlated with the reduction of glaucomatous optic neuropathy. Public health figures estimate that 2.5 million Americans manifest ocular hypertension.
In glaucoma associated with an elevation in eye pressure the source of resistance to outflow is in the trabecular meshwork. The tissue of the trabecular meshwork allows the “aqueous” to enter Schlemm's canal, which then empties into aqueous collector channels in the posterior wall of Schlemm's canal and then into aqueous veins. The aqueous or aqueous humor is a transparent liquid that fills the region between the cornea at the front of the eye and the lens. The aqueous humor is constantly secreted by the ciliary body around the lens, so there is a continuous flow of the aqueous humor from the ciliary body to the eye's front chamber. The eye's pressure is determined by a balance between the production of aqueous and its exit through the trabecular meshwork (major route) or via uveal scleral outflow (minor route). The trabecular meshwork is located between the outer rim of the iris and the internal periphery of the cornea. The portion of the trabecular meshwork adjacent to Schlemm's canal causes most of the resistance to aqueous outflow (juxtacanilicular meshwork).
Glaucoma is grossly classified into two categories: closed-angle glaucoma and open-angle glaucoma. The closed-angle (glaucoma is caused by closure of the anterior angle by contact between the iris and the inner surface of the trabecular meshwork. Closure of this anatomical angle prevents normal drainage of aqueous humor from the anterior chamber of the eye. Open-angle glaucoma is any glaucoma in which the angle of the anterior chamber remains open, but the exit of aqueous through the trabecular meshwork is diminished. The exact cause for diminished filtration is unknown for most cases of open-angle glaucoma. However, there are secondary open-angle glaucomas that may include edema or swelling of the trabecular spaces (from steroid use), abnormal pigment dispersion, or diseases such as hyperthyroidism that produce vascular congestion.
All current therapies for glaucoma are directed at decreasing intraocular pressure. This is initially by medical therapy with drops or pills that reduce the production of aqueous humor or increase the outflow of aqueous. Surgical therapy for open-angle glaucoma consists of laser (trabeculoplasty), trabeculectomy and aqueous shunting implants after failure of trabeculectomy or if trabeculectomy is unlikely to succeed. Trabeculectomy is a major surgery that is most widely used and is augmented with topically applied anticancer drugs such as 5-flurouracil or mitomycin-c to decrease scarring and increase surgical success.
Other means to treat glaucoma and ocular hypertension, involve the administration of drugs to the eye. A conventional method of drug delivery is by topical drop application to the eye's surface. Topical eye drops, though effective, can be inefficient. For instance, when an eye drop is instilled in an eye, it often overfills the conjunctival sac (i.e., the pocket between the eye and the lids) causing a substantial portion of the drop to be lost due to overflow of the lid margin and spillage onto the cheek. In addition, a large portion of the drop remaining on the ocular surface can be washed away into and through a lacrimal canaliculus, thereby diluting the concentration of the drug before it can treat the eye. Further, in many cases, topically applied medications have a peak ocular effect within about two hours, after which additional applications of the medications should be performed to maintain the therapeutic benefit. PCT Publication WO 06/014434 (Lazar), which is incorporated herein by reference in its entirety, may be relevant to these or other issues associated with eye drops.
Compounding ocular management difficulty, patients often do not use their eye drops as prescribed. Noncompliance rates of at least 25% are reported. This poor compliance can be due to discomfort and the normal reflex to protect the eye. Therefore, one or more drops may miss the eye. Older patients may have additional problems instilling drops due to arthritis, unsteadiness, and decreased vision. Pediatric and psychiatric populations pose difficulties as well.
Lacrimal implants are devices that are inserted into a punctum and an associated lacrimal canaliculus of an eye, either to block drainage of tears (to prevent conditions such as dry eye), or to contain a quantity of drug for release into the eye.
FIGS. 1-2 illustrate example views of anatomical tissue structures associated with an eye 100. Certain of the anatomical tissue structures shown may be suitable for treatment using the various lacrimal implants and methods discussed herein. The eye 100 is a spherical structure including a wall having three layers: an outer sclera 102, a middle choroid layer 104 and an inner retina 106. The sclera 102 includes a tough fibrous coating that protects the inner layers. It is mostly white except for the transparent area at the front, commonly known as the cornea 108, which allows light to enter the eye 100.
The choroid layer 104, situated inside the sclera 102, contains many blood vessels and is modified at the front of the eye 100 as a pigmented iris 110. A biconvex lens 112 is situated just behind the pupil. A chamber 114 behind the lens 112 is filled with vitreous humor, a gelatinous substance. Anterior and posterior chambers 116 are situated between the cornea 108 and iris 110, respectively and filled with aqueous humor. At the back of the eye 100 is the light-detecting retina 106.
The cornea 108 is an optically transparent tissue that conveys images to the back of the eye 100. It includes a vascular tissue to which nutrients and oxygen are supplied via bathing with lacrimal fluid and aqueous humor as well as from blood vessels that line the junction between the cornea 108 and sclera 102. The cornea 108 includes a pathway for the permeation of drugs into the eye 100.
Turing to FIG. 2, other anatomical tissue structures associated with the eye 100 including the lacrimal drainage system, which includes a secretory system 230, a distributive system and an excretory system, are shown. The secretory system 230 comprises secretors that are stimulated by blinking and temperature change due to tear evaporation and reflex secretors that have an efferent parasympathetic nerve supply and secrete tears in response to physical or emotional stimulation. The distributive system includes the eyelids 202 and the tear meniscus around the lid edges of an open eye, which spread tears over the ocular surface by blinking, thus reducing dry areas from developing.
The excretory system of the lacrimal drainage system includes, in order of flow, drainage, the lacrimal puncta, the lacrimal canaliculi, the lacrimal sac 204 and the lacrimal duct 206. From the lacrimal duct 206, tears and other flowable materials drain into a passage of the nasolacrimal system. The lacrimal canaliculi include an upper (superior) lacrimal canaliculus 208 and a lower (inferior) lacrimal canaliculus 210, which respectively terminate in an upper 212 and lower 214 lacrimal punctum. The upper 212 and lower 214 punctum are slightly elevated at the medial end of a lid margin at the junction 216 of the ciliary and lacrimal portions near a conjunctival sac 218. The upper 212 and lower 214 punctum are generally round or slightly ovoid openings surrounded by a connective ring of tissue. Each of puncta 212, 214 leads into a vertical portion 220, 222 of their respective canaliculus before turning more horizontal at a canaliculus curvature 250 to join one another at the entrance of the lacrimal sac 204. The canaliculi 208, 210 are generally tubular in shape and lined by stratified squamous epithelium surrounded by elastic tissue, which permits them to be dilated. As shown, a lacrimal canaliculus ampulla 252 exists near an outer edge of each canaliculus curvature 250.
For numerous reasons (e.g., the size, shape, positioning, and materials of some conventional lacrimal implants, and variability in punctum size and shape), retention of the implants in the punctum and associated lacrimal canaliculus has been inconsistent. Users of lacrimal implants may inadvertently dislodge the lacrimal implant by wiping their eye. Further, some configurations of lacrimal implants may dislodge themselves, such as when a user sneezes, or tears excessively.
Accordingly, it is desirable to have a lacrimal implant that solves these problems and provides improved retention across different sizes of puncta.